1. Field of the Invention
The present invention generally relates to window coverings and treatments. More specifically, the present invention relates to a tensioning device suitable for use in tensioning window covering lift cords.
2. Description of the Related Art
Coverings for architectural openings such as windows, doors, archways and the like take numerous forms, including conventional draperies, horizontal venetian blinds, vertical blinds, roll up shades and other coverings. The control systems utilized to operate these coverings vary depending upon the type of covering, so that a roll up shade, for example, would normally have a different control system than a vertical blind or a horizontal venetian blind. Most control systems are operated with pull cords, pull tapes, or tilt wands that hang from an end of a head rail and are manipulated by a human operator to move the covering between extended and retracted positions.
One known control system employs one or more lift cords that extend downward through the covering from the head rail to a bottom rail. The lift cords are typically wound around an axle in the head rail, which can be rotated to take-up or let-out the lift cords to extend or retract the covering. The weight of the bottom rail keeps the lift cords under tension, preventing them from tangling or looping onto themselves or other objects in the head rail. When an upward force is applied to the bottom rail, the tension in the lift cords is lost, allowing the cords to become tangled in the head rail.
Therefore, a need exists for a means to maintain tension in the portion of the lift cord that resides in the head rail, regardless of the forces applied to the bottom rail.
A lift cord tensioning device is provided for use in a window covering having at least one lift cord that extends downward though a shade portion from a head rail to a bottom rail. In one embodiment of the present invention, the tensioning device includes a pliable material having an aperture through which the lift cord extends. The aperture is sized to resist passage of the lift cord such that tension remains on the portion of the lift cord that resides in the head rail even when an upward directed force is applied to the bottom rail.
In an alternate embodiment of the present invention, the tensioning device includes a pair of holes through which the at least one lift cord extends. The holes are offset from one another a distance sufficient to resist passage of the lift cord such that tension remains on the portion of the lift cord that resides in the head rail.
In another alternate embodiment of the present invention, the tensioning device includes a moveable gate member and a fixed gate member between which the lift cord extends. The moveable gate member is biased toward the fixed gate member and into frictional contact with the lift cord. The biasing force against the moveable gate selected to yieldably resist passage of the lift cord.
The present invention allows the weight of the bottom rail to pull the lift cord down into the shade portion of the window covering, but substantially prohibits the lift cord from raising back into the head rail except through normal operation.